Many types of disposable absorbent products, such as diapers, training pants, adult incontinence devices, sanitary napkins, panty liners, and the like, are available that have a high capacity for absorbing urine and other body exudates. Disposal products of this type generally comprise some sort of liquid-pervious topsheet material, an absorbent core, and a liquid-impervious backsheet material. Although these types of absorbent articles may be highly efficient for the absorption of liquids, it is generally known that skin under the absorbent article is more susceptible to skin disorders, including diaper rash or diaper dermatitis, erythema (i.e., redness), heat rash, abrasion, pressure marks and skin barrier loss. Diaper rash is a common form of irritation and inflammation of those parts of an infant""s body normally covered by a diaper. It is generally accepted that diaper rash or diaper dermatitis is a condition which begins as a contact irritant dermatitis. The commonly known factors linked to diaper dermatitis include ammonia, bacteria, products of bacterial action, urine pH, candida albicans, and moisture. This irritation and/or inflammation result from extended contact of the skin with urine, feces, or both. When absorbent articles are worn to catch and hold the body exudates, the absorbent articles not only hold the skin of the wearer in direct contact with irritants in the body exudates, but also hold the skin in an occluded condition. Often, the skin is subjected to such a condition for extended periods of time, that is, until the soiled article is changed. As the skin under the absorbent article becomes overhydrated or irritated by such prolonged and repeated exposures, the skin condition is compromised, i.e., the skin is injured and/or becomes more susceptible to skin disorders or damages. While this condition is certainly more common in infants, it is not limited to infants. Similar conditions occur in, for example, incontinent or bed-ridden adults.
Common approaches to the improvement of skin conditions in the diapered areas often focus on reducing skin hydration, such as frequent changing of diapers, using moisture absorbing powders, using superabsorbent materials, and improving air flow in diapers, and the like.
Another common approach is to apply a topical cream, ointment, lotion or paste to the affected areas. This procedure usually provide some degree of physical barrier protection to the skin against direct contact with fecal or urine irritants. However, the barrier approach may be occlusive in itself, thus not very effective once a full blown case of diaper dermatitis has developed. There is a tendency to slather on a thick layer of the diaper rash cream or ointment, which is occlusive, messy, wasteful and aesthetically displeasing. Moreover, the excess cream/ointment may transfer to the absorbent article or other clothing, such as underwear, leading to reduced absorbency or stained clothing. This procedure is also time-consuming and often forgotten. Furthermore, the cream/ointment typically comes in a reusable container and is hand-applied to the skin. The composition often has a thick, greasy and tacky consistency in order to remain on the infant""s skin, the residual composition is not easily removed from the opening of the container or the hands of the care-giver, and the possibility of cross contamination between one infant to another is increased.
An alternative approach attempts to simultaneously address multiple causes or important cofactors by using a multi-ingredient skin care composition. The composition may include barrier substances, skin conditioning agents or emollients, and may even include various skin care ingredients.
The skin care ingredients may exist as insoluble particles suspended in the substantially oleagineous compositions due to their limited solubility in the oleagineous substances. Furthermore, these solid particles generally have densities much higher than the oleagineous matrix that they are dispersed in. For example, common commercial diaper rash creams or ointments comprise zinc oxide particles dispersed in an organic matrix. Zinc oxide has a density of about 5.7 g/cm3 while the density of organics is generally about 0.9 g/cm3. This large difference in densities often leads to separation and processing problems.
A good suspension of the skin care ingredients in the lotion composition is highly desirable. As used herein, a xe2x80x9cgoodxe2x80x9d suspension means the particulate substances are substantially uniformly dispersed in the medium, and the dispersion is stable, i.e., no visible stratification, agglomeration or settling with the passage of time. Uniform distribution of the ingredients minimizes variation in product quality and assures that every application of the product to the skin delivers a sufficient amount of ingredients to achieve efficacy. There is no need to over-apply the product in order to achieve the desired benefits; consequently, there is less waste. Therefore, a good suspension provides the most efficient delivery of these skin care ingredients to the skin and maximizes the skin benefits. Moreover, there is no need to incorporate an extra amount of the costly ingredients to ensure efficacy; thus, an effective composition can be made at lower cost. Additionally, a good suspension also reduces the lumpiness of the lotion and provides a smooth skin feel when applied.
Generally, a suspension of particulates in a Newtonian fluid follows the Stokes law, which states that the rate of separation or settling is proportional to the density difference between the suspended particles and the suspending medium, to the square of the particle size of the suspended particles, and is inversely proportional to the viscosity of the medium. Agglomeration and gravitational settling are often observed when particulate materials are suspended in a Newtonian fluid, causing problems in storage, transportation and processing of these compositions. Where a batch process is used, the agglomeration and settling can occur in a holding tank. Moreover, as the composition flows through processing equipment, the agglomerates, formed either in the holding tank or along the process, tend to get hung up in various elements having small diameters (such as pipes, valves, slots) along the processing line. This xe2x80x9cbridgingxe2x80x9d problem often causes clogged orifices, openings, slots and/or narrow pipes, and can severely reduce or even stop the flow of the composition through the processing equipment.
Agitation or turbulent flow can redisperse the suspended particles and avoid agglomeration and settling problems. It is known that the flow of a liquid through a pipe or like elements may be laminar or turbulent, and the transition from a laminar flow to a turbulent flow depends on the properties of the fluid, its velocity and the diameter of the pipe. However, agitation, velocity and pipe diameter are processing parameters that are constrained to a limited range for a given piece of equipment. Variations of these parameters within the equipment-limiting range often fail to solve the problem.
A variety of rheological agents, such as thickeners, thixotropic agents and dispersing agents, can be added to such a composition to alter the rheological properties of the composition. These rheological agents serve to improve the stability of the suspensions and to maintain the viscosity at a desired level for a wide range process conditions and end-use situations.
Creams or ointments containing particles of zinc oxide, anti-microbials, or protease or enzyme inhibitors are known. These compositions have traditionally been prepared as oil-in-water or water-in-oil emulsions. These emulsions are not very effective in improving the condition and/or appearance of the diapered skin, particularly when the composition is delivered via a vehicle such as an absorbent article. The absorbent core element may draw the aqueous phase away from the surface of the article thereby reducing the skin benefits provided by the composition. Additionally, the oil phase, being pulled along, may interfere with the absorbency of the core. Anhydrous compositions are also known, which typically include volatile liquid carriers, such as silicone or solvents. The volatile materials can cause irritation or burning to the skin and these effects are especially acute when skin is already injured or compromised due to chronic exposure to body exudates. Moreover, the vapors from the volatile materials can become entrapped between the skin and the absorbent article worn close to the skin, further exacerbating the irritation or burning effects. Exemplary creams or ointments are disclosed in U.S. Pat. No. 4,556,560 issued Dec. 3, 1985 to Buckingham; U.S. Pat. No. 5,091,193 issued Feb. 25, 1992 to Enjolras et al.; U.S. Pat. No. 5,110,593 issued May 5, 1992 to Benford; U.S. Pat. No. 5,362,488 issued Nov. 8, 1994 to Sibley et al.; and U.S. Pat. No. 5,618,522 issued Apr. 8, 1997 to Kaleta et al.
Products containing the FDA monographed skin care ingredients are commercially available, such as A and D(copyright) Ointment, Vaseline(copyright) Petroleum Jelly, Desitin(copyright) Diaper Rash Ointment and Daily Care ointment, Gold Bond(copyright) Medicated Baby Powder, Aquaphor(copyright) Healing Ointment, Baby Magic(copyright) Baby Lotion, Johnson""s Ultra Sensitive Baby Cream. These commercial products have a major disadvantage that they are creams or ointments, i.e., they are flowable at room temperature such that they can not be immobilized on the surface of an absorbent article and interfere with the absorbency of the article.
It is also known that solid or semi-solid compositions can be provided by using either solidifiable carriers or hardeners (e.g., petrolatum, waxes). For example, U.S. Pat. No. 5,194,261 issued Mar. 16, 1993 to Pichierri. The Pichierri reference discloses a semi-solid which functions as a thick, adhesive and barrier layer over the skin. The ointment has a thick and sticky consistency. An additional barrier layer is applied over the ointment. The major disadvantage of Pichierri reference is stickiness and the occlusiveness of the ointment and the barrier layer. Moreover, it does not contain the skin care ingredients of the present invention, nor the rheological agent to suspend the skin care ingredients and to prevent settling. U.S. Pat. No. 4,911,932 issued Mar. 27, 1990 to Clum et al. The Clum reference teaches compositions containing specific imidazole derivatives and zinc oxide. The Clum reference does not disclose automatic transfer (i.e., without manual application) of the composition to the skin, nor a delivery vehicle for the composition, nor how to successfully dispose the composition and immobilize it on the skin-contacting surface of the delivery vehicle.
Articles treated or impregnated with skin care compositions are also known. For example, U.S. Pat. No. 3,896,807 issued Jul. 29, 1975 to Buchalter discloses an article impregnated with a solid oil phase of cream formulation which forms a cream upon addition of moisture thereto. A major disadvantage of the article disclosed by the reference is that transfer of a beneficial substance from the absorbent substrate to skin is delayed and is only realized when body fluids are released. Additionally, the reference composition does not contain skin care ingredients for skin care benefits nor rheological agents to suspend them and to prevent them from settling. U.S. Pat. No. 5,525,346 issued Jun. 11, 1996 to Hartung et al. discloses an absorbent article having oil-in-water emulsions comprising a non-ionic emulsifier, a dimethicone, sodium citrate/citric acid buffer system, aloe vera, preservatives and water. The major disadvantage of the reference that the aqueous phase may be drawn away from the surface by the absorbent element of the article, resulting in reduced effectiveness of the emulsions for skin benefits and interference with the absorbency of the article. U.S. Pat. No. 5,643,588 issued Jul. 1, 1997 and U.S. Pat. No. 5,635,191 issued Jun. 3, 1997, both to Roe et al., U.S. Pat. No. 5,607,760 issued Mar. 4, 1997, and U.S. Pat. No. 5,609,587 issued Mar. 11, 1997, both to Roe, disclose disposable absorbent articles having a lotion composition disposed on the topsheet; the lotion composition comprises an emollient and an immobilizing agent. The major disadvantage of the references is that the compositions do not contain skin care ingredients of the present invention nor rheological agents to suspend them and to prevent settling. U.S. patent application Ser. No. 09/041,509, filed Mar. 12, 1998 by McOsker et al., U.S. patent application Ser. No. 09/041,232, filed Mar. 12, 1998 by Rourke et al. and U.S. patent application Ser. No. 09/041,266, filed Mar. 12, 1998 by Roe et al., disclose skin care ingredients that are incorporated into an absorbent article directly or via an delivery vehicle, wherein the skin care ingredients are either neat or in a composition. The major disadvantage of the references is that the compositions contain no rheological agent to stabilize the skin care composition and are unsuitable for the processing/converting operation.
There remains a need for an improved skin care composition which comprises skin care ingredients specifically beneficial to diapered skin, and has a desirable rheological profile over a temperature range from processing temperature to room temperature. Specifically, the composition is a stable and processable suspension at the processing temperature and it becomes solid or semi-solid when cooled. Moreover, the composition becomes a solid or semi-solid when cooled and immobilized on a substrate surface, yet it is readily transferable to skin upon contact with body heat, normal wear motion and/or friction.
It is desirable to modify the viscosity and the elastic modulus of a skin care composition with rheological agents such that the skin care ingredients remain suspended in the composition with insubstantial agglomeration, stratification and/or settling during processing, transportation and storage.
It is also desirable that the composition becomes a solid or semi-solid when cooled, and that the composition is readily transferable to the skin it contacts.
Additionally, it is desirable that the composition may be efficiently and esthetically applied to the skin via a delivery vehicle such as an absorbent article.
It is further desirable to provide a process for making an absorbent article having a stable skin care composition on a skin-contacting surface of the absorbent article.
The present invention relates to an absorbent article having a stable skin care composition disposed on at least a portion of its skin-contacting surface. The skin care composition is readily transferable to the skin via normal contact, wearer motion, and/or body heat. The skin care composition contains at least one skin care ingredient imparting skin benefits to the skin upon transfer to the skin and at least one rheological agent for stabilizing the composition such that agglomeration, stratification and/or settling are minimized.
It has been found that the rheological properties of the composition can be modified with suitable rheological agents to provide a substantially stable suspension at the processing temperature such that it can be applied to a skin-contacting surface of an absorbent article in a continuous or a batch process. Suitable compositions typically have an elastic modulus of at least about 5 dynes/cm2 (measured at a strain rate of 0.2%, an oscillation frequency of 10 rad/sec and a temperature of 77xc2x0 C.). When cooled, the composition becomes a solid or semi-solid such that it is substantially non-flowable and remains xe2x80x9clocked-inxe2x80x9d on the skin-contacting surface of the absorbent article, yet it is readily transferable to a wearer""s skin via contact, normal wearer""s motion, and body heat.
The present invention also relates to a process for making the absorbent articles having a substantially stable skin care composition disposed thereon. The rheological agent modifies the viscosity of the composition and stabilizes the composition. The substantially stable composition can be readily transported through pipes, slots, or other elements of a processing equipment without the suspended particulates settling out or building up in the equipment. The composition can remain substantially stable even in the stationary state, e.g., while in the holding tank or in storage. Furthermore, the composition can be easily applied to a surface of a substrate without the particulates plugging up the application element of the processing equipment. Additionally, the stable lotion composition can be applied to a substrate surface in a continuous or batch process to deliver a fairly constant concentration of skin care ingredients onto the substrate surface and produce products of consistent quality throughout the run.